Some objects become hot when exposed to external heat sources such as sunlight and fire. Some other objects become hot as a result of internal heat sources such as for example, a soldering iron that turns hot as a result of passage of an electric current through a heater coil inside the soldering iron. In the case of the soldering iron, it is desirable to generate heat for purposes of soldering. However, in some other cases it is undesirable to generate heat in an object because heating contributes to various adverse conditions such as reduced operating efficiency and reduced mean time between failures (MTBF). It is particularly undesirable to allow certain types of electronic components to run excessively hot when in operation. For example, it is undesirable to allow an integrated circuit (IC) to run excessively hot, because excessive heating can lead to a reduced MTBF and reduced operating efficiency of the IC. Traditionally, the adverse effects of excessive heating of an electronic component such as an IC, has been addressed by the use of a heat sink.
In one traditional solution, a heat sink includes a metal plate having a number of metal fins projecting upwards from the metal plate. The metal plate, which is affixed to a top surface of the IC by using a heat sink compound, conducts heat upwards from the IC and into the fins. Ambient air above the IC then dissipates the heat in the fins.
In another traditional solution, that is illustrated in FIG. 1, a heat sink 105 made of a heat conducting material such as aluminum, is attached to a top surface of an IC 110. The heat sink 105 includes a number of openings through which a cooling agent such as water, is allowed to flow on to the top surface of the IC 110. Heat from the top surface of the IC 110 is transferred to the water, which then flows laterally out of the heat sink 105 via an exit opening 106. The lateral flow of water out of the heat sink 105 interferes with the water flowing into the heat sink 105, thereby leading to turbulence, which in turn impedes the flow of water out of the exit opening 106. Consequently, the IC 110 is not cooled to an optimal extent.
In an alternative traditional solution, some of the deficiencies of the heat sink 105 is remedied by using a heat sink 235 that is shown in FIG. 2. The heat sink 235 has a multi-level structure that is typically manufactured by using IC fabrication techniques such as etching and patterning upon each of a number of silicon layers. In this solution, a first silicon layer 220 of the heat sink 235 has a number of large sized holes (such as hole 205) through which water is fed downwards into the heat sink 235. The water then flows laterally into a number of holes in the second silicon layer 225 (such as hole 210). The size of the holes in the second silicon layer 225 is smaller than that of the holes in the first silicon layer 220, thereby increasing water pressure in the flow of water through the second silicon layer 225 and on to a third silicon layer 230. The third silicon layer 230 has another set of holes (such as hole 215), each of which is even smaller in size than the holes in the second silicon layer 225, thereby increasing water pressure even further. Fewer or more layers can be used in order to obtain a desirable level of water pressure upon the top surface of the IC 240.
Heat from the top surface of the IC 240 is transferred to the water and the heated water then flows in the opposite direction (upwards) through the third silicon layer 230, the second silicon layer 225, and the first silicon layer 220. Some of the heat in the heated water is transferred into each of the silicon layers as the heated water flows upwards. Because silicon is a relatively good conductor of heat, the heat transferred into the silicon layers by the exiting water, leads to an increase in temperature in the incoming water flowing downwards through the silicon layers and towards the top surface of the IC 240, thereby reducing the cooling efficiency of the heat sink 235.